feat: Add SQL support for TRY_CAST function

[alexander-beedie]

Added SQL support for the TRY_CAST function (as implemented by various¹ databases).

Example

import polars as pl
df = pl.DataFrame({"n": [-10, 0, 10, 20]})

Strict (default) CAST fails on invalid values ...

df.sql("SELECT CAST(n AS uint1) FROM df")
# ComputeError: conversion from `i64` to `u8` failed in column 'n' for 1 out of 4 values: [-10]

... whereas TRY_CAST replace invalid values with null:

df.sql("SELECT TRY_CAST(n AS uint1) FROM df")
# shape: (4, 1)
# ┌──────┐
# │ n    │
# │ ---  │
# │ u8   │
# ╞══════╡
# │ null │
# │ 0    │
# │ 10   │
# │ 20   │
# └──────┘

Footnotes

1. TRY_CAST: SQL Server, DuckDB ↩

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.48%. Comparing base (ef1c0c8) to head (2097e7e).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16589      +/-   ##
==========================================
- Coverage   81.50%   81.48%   -0.02%     
==========================================
  Files        1414     1414              
  Lines      185612   185619       +7     
  Branches     2997     2997              
==========================================
- Hits       151288   151259      -29     
- Misses      33808    33844      +36     
  Partials      516      516              

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